The regularly recurring incidence of natural sleep forms one of the most important subjects for physiological investigation. Were it an event of rare occurrence, it would excite a degree of astonishment and alarm equal to the agitation now experienced by the spectator of an ordinary attack of syncope or of epileptic convulsion. But, so completely does the recurrence of sleep harmonize with all the other facts of life that we are as indifferent to its nature as we are to every other healthy function of the body. It is only when the mind has undertaken a critical observation of the bodily and mental changes which accompany and condition the phenomenon that we begin to comprehend its wonderful character. Ushered in by a waning activity of body and mind that no effort of the will can long resist, nothing could more forcibly suggest the idea of approaching dissolution if, from the very earliest period of unconscious infancy, we had not been accustomed to the dominion of this imperious necessity. The remarkable likeness between the fading of consciousness in sleep and its extinction in death has, in all ages and among all people, arrested the attention of poets and philosophers of every degree.

Soft repose,
A living semblance of the grave,

sang old Thomas Miller; and, describing, in Milton’s stately verse, the close of his first day in the garden of Eden, Adam says:

Gentle sleep
First found me, and with soft oppression seized
My drowsy sense, untroubled, though I thought
I then was passing to my former state
Insensible, and forthwith to dissolve.
How wonderful is death,
Death and his brother, Sleep!

exclaims Shelley, echoing the marvellous strains that have come down to us from the days of Homer and Hesiod. In that venerable literature Sleep and Death are represented as twin brothers, sons of Night; dwelling in the lower world of spirits, whence they come forth to perform the will of the Olympian Gods.

The prosaic genius of our scientific generation no longer tolerates such lively exercise of the imagination. The splendid anthropomorphism of the Hebrew poet, looking out upon the silent night, and cheering his soul with the sonorous exclamation,

Behold, he that keepeth Israel
Shall neither slumber nor sleep
·····
For so he giveth his beloved sleep,

has become a mere memory of childhood. Wordsworth understood the full significance of this change when he wrote:

There was a time when meadow, grove, and stream,
The earth, and every common sight,
To me did seem
Apparelled in celestial light,
The glory and the freshness of a dream.
It is not now as it has been of yore;
Turn whereso’er I may,
By night or day,
The things which I have seen I now can see no more!
... I know, where’er I go,
That there has passed away a glory from the earth.

If, however, despite the loss of much that was beautiful and attractive in the myths of antiquity, we take advantage of the

Years that bring the philosophic mind,

we shall surely find in the scientific investigation of sleep enough to awaken “thoughts too deep for” words.